Bodily cancers are commonly treated using radiation therapy. Radiation therapy employs high energy radiation to kill cancer cells. One type of radiation therapy is brachytherapy, in which a source of radiation is in direct contact with an afflicted tissue. A common brachytherapy treatment, transperineal seed implantation, involves placing radioactive seeds in the prostate gland to kill prostate gland cancer cells. A physician employs tools such as ultrasound, computerized axial tomography (“CAT”) scans, and X-ray images in concert with dose-planning computer software programs to evaluate the medical condition of a patient. The physician constructs an optimal treatment plan to evenly distribute radiation throughout the afflicted tissue. Radioactive seeds of discrete radioactive strengths are inserted through multiple implantation needles at positions in the prostate gland corresponding to the treatment plan. Multiple implantation needles are required to insert the radioactive seeds into multiple locations in the afflicted tissue, with each needle containing a specified arrangement of the radioactive seeds. Non-radioactive spacers between the radioactive seeds are used to achieve a desired placement of the radioactive seeds specified by the physician's treatment plan.
The implantation needles are accurately located in the prostate gland utilizing a grid template and ultrasound visualization of the implantation needles once they are inserted into the prostate gland. The eventual position of the radioactive seeds and spacers (if utilized) is inferred from the position of the carrier implant needle prior to withdrawal. This procedure is detailed in an article entitled “Ultrasound Guided Transperineal Implantation for the Treatment of Early Stage Prostate Cancer” by Grimm, Blasko, and Ragde, in The Atlas of The UrologicalClinics of North America, Vol. II, No. 2, October 1994. In 2000, roughly 35% of all men diagnosed with localized prostate gland cancer were treated with radioactive seed implants compared with only about 4% in 1995. Radioactive seed implants have gained widespread acceptance due to the many patient benefits, including long-term results comparable with alternative therapies such as radical prostatectomy and external beam radiation therapy without the degree of impotence and incontinence seen following treatment.
In the radioactive seed implant technique, exact positioning of the radioactive seeds is critical to ensuring that the radiation dose delivered to the prostate gland matches the radiation dose prescribed in the physician's treatment plan. As one shortcoming, the radioactive seed implant technique does not prevent the movement of the radioactive seeds in the prostate gland once the implantation needle is removed. Radioactive seeds can migrate within the prostate gland after implantation, and can even move outside the confinement of the prostate gland. As another shortcoming, the initial radioactive seed positioning can be influenced by the technique used to withdraw the implantation needle, whereby the radioactive seeds and spacers are drawn along the implantation needle track as the implantation needle is removed from the prostate gland.
Horowitz (U.S. Pat. No. 4,815,449) describes a radioactive seed delivery system comprising an elongated member made of bioabsorbable material with radioactive seeds dispersed within the elongated member. The elongated member is essentially non-deflecting and is designed for direct insertion into the prostate gland. As one shortcoming, the radioactive seed delivery system does not allow for a variable positioning of the radioactive seeds. As another shortcoming, the radioactive seed delivery system is expensive to realize due to the cost of the process of encapsulating the radioactive seeds within the elongated member.
Grimm (U.S. Pat. Nos. 6,010,446 and 6,450,939) describes spacer elements manufactured from a bioabsorbable material comprising a center section and two cup-like end sections. The cup-like end sections serve to directly hold and receive adjacent radioactive seeds. A series of radioactive seeds and spacer elements form an integral unit which would maintain the relative position of the radioactive seeds in the prostate gland. The spacer elements ensure radioactive seed location following implantation. As one shortcoming, the spacer elements do not easily allow for a variable distance of separation between adjacent radioactive seeds without manufacturing and distributing different size spacer elements for every possible radioactive seed spacing required by a treatment plan.
Thus, a need exists for enhanced spacer elements to separate and hold seeds.